Features - February 2015

Advancing Fuel Cells through Advanced Manufacturing

Advanced manufacturing is reshaping the way industry builds parts and components, and energy researchers at the National Energy Technology Laboratory (NETL) are using this transformative approach to dramatically improve power production from solid oxide fuel cells (SOFCs).  

FuelCellTeam.jpgDrs. Abernathy and Lee investigate reactions inside a SOFC stack using the DOE Fuel Cell Test Stack facility at NETL in Morgantown, WV.

Advanced manufacturing literally breaks the mold, offering layer by layer construction of everything from stencils to precision engine components while avoiding expensive, cumbersome molds that restrict customization, limit what materials can be used, and nix complex configurations. Now the options are limitless. Advanced manufacturing incorporates precise computer models to enable construction of intricate products, using a broad range of materials, and endless options for configuration. If you can imagine it, advanced manufacturing can make it a reality. Advanced manufacturing techniques are more cost-efficient than conventional manufacturing techniques, don't waste material, and are much more precise. For NETL's fuel cell researchers, the precision of advanced manufacturing is revolutionizing the way fuel cell cathodes are made and enabling a better option for clean, affordable energy from coal. 

NETL's fuel cell team has invented an advanced manufacturing technique to engineer special structures inside a SOFC to optimize the location and intensity of the power-producing reactions. Let's take a closer look.

What Is a Solid Oxide Fuel Cell?

Like all fuel cells, SOFCs are electrochemical devices that convert the chemical energy of a fuel (such as methane) and oxidant (such as air) directly into electrical energy. And, like all fuel cells, SOFCs consist of two electrodes—an anode and a cathode—joined together by an electrolyte, which separates the electrode reactions to produce electricity.  

Fuel-Cell2-01.jpgSOFC--1-of-2-.jpg

Fuel cells convert chemical energy into electricity. Shown here is a 10 watt solid oxide fuel cell.

What makes SOFCs ideal for fossil energy applications is that they can use both hydrogen and carbon monoxide, which are produced during coal gasification, in the electrochemical reaction. Since SOFCs do not operate through a combustion process, they are much more efficient and environmentally benign than conventional electric power generation processes. In fact, SOFCs are uniquely suited to generate clean electric power directly from fossil energy sources with maximum efficiency and with minimal environmental impact.

However, reliability and affordability have traditionally impeded SOFCs from gaining broad commercial interest. SOFCs are expensive and, because they operate at high temperature, tend to degrade quickly. To better understand how to improve these factors, NETL researchers investigated how and where the chemical reactions took place within SOFCs. What they discovered is that cathode performance can significantly impact the overall performance and cost of a fuel cell system.

Cathode Infiltration for Increased Efficiency

To improve cathode efficiency, NETL researchers developed a technique known as infiltration, in which an electrocatalyst is deposited on the cathode in the precise location needed to facilitate reactions and improve the ratio of electricity produced to fuel consumed. In the lab, the electrocatalyst is applied by hand to each individual cell, but this obviously poses great limitations for applying cathode infiltration to mass production of SOFCs. 

Traditional SOFC manufacturing processes like screen printing limit control over where a fuel cell's active sites (the sites where reactions occur) will be distributed.  In screen printing, liquid "paints" generated from source powders are printed onto the cell, much like printing a design onto a t-shirt. While SOFCs produced this way are cheap and the electrodes are produced with uniform size and shape, on a microscopic level—which is where the critical reactions occur for the electrocatalyst—screen printing results in unpredictable and sometimes inconsistent structures. A more precise manufacturing method was needed if cathode infiltration was to be a practical solution to improving SOFC performance and efficiency.

Building a Better Fuel Cell

This is where NETL researchers turned to advanced manufacturing to engineer more ideal and precise cathode configurations. Their investigations of the internal SOFC structure resulted in complete and detailed 3-D maps of active components, and they applied that knowledge to determine exactly where the electrocatalyst should be placed for optimal performance.

Using advanced manufacturing concepts, the NETL engineers designed a novel process that uses a spray coating machine coupled with special computer software to mass produce infiltrated SOFCs possessing a precisely controlled electrode structure. The cathode can be built layer by layer, starting with an inexpensive backbone made by screen printing, and then placing active structures at the exact location for optimal functionality so that the reaction networks are constructed in a sequential way. By controlling how the structure is manufactured, the reaction networks can be engineered for improved efficiency, which will ultimately lower cell costs and push SOFCs into the commercial market.   

SOFC--2-of-2-.jpgNETL's sonic spray-coating machine deposits electrocatalyst solution on button SOFCs.

Advanced manufacturing techniques enabled the NETL research team to control the structure and engineer optimal performance. The team designed a "super-cathode," and advanced manufacturing processes enabled its production. Using their advanced manufacturing technique, researchers are now able to cheaply and precisely control how much infiltrate is applied to achieve the desired performance. The result is new fuel cells that cost less per kilowatt generated, are more efficient, and more durable.

Balancing Tomorrow's Energy Mix

NETL's innovations are positioning SOFCs to provide clean, efficient energy from abundant coal resources, and SOFCs offer additional benefits to our power generation portfolio as well. When future fuel cell systems are integrated into the nation's power grid, SOFCs could enable greater use of renewable energy sources because these future SOFCs will respond to power fluctuations that result from variable sources, such as wind and solar, and provide power to balance these intermittent energy sources. When incorporated into advanced coal-based systems, such as integrated gasification-fuel cell plants, SOFCs offer unmatched efficiency, less CO2 produced per megawatt of electricity, lower water consumption, and more electricity per pound of coal.

Innovative approaches to how products are made helps position our manufacturing industry to create products with unimagined capabilities and functions. NETL's energy researchers are shaping not only how technologies are manufactured, but also how the nation produces and uses energy.